Adhesive transfers



April 28, 1964 F. w. MAcKENzlE 3,131,106

ADHESIVE TRANSFERS Filed June 22, 1961 FIG. l

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United States Patent O 3,131,106 ADHESIVE TRANSFERS Frederick WilsonMackenzie, London, England, assigner to Letraset Limited, London,England, a British company Filed June 22, 1961, Ser. No. 118,765 Claimspriority, application Great Britain June 24, 1960 Claims. (Cl. 156-230)This invention relates to adhesive transfers (decalcomanias) and moreparticularly to a form of transfer material in which an image, design orprinted matter (hereinafter generally referred to as indicia) may betransferred from a carrier sheet to a further support. The inventionincludes transfer materials, their production and the processes of theiruse.

Transfer materials consisting of a carrier sheet carrying an indiciawhich can be transferred bodily from the carrier sheet to a furthersupport are very well known indeed and a. great deal of effort has beendirected to the production of such materials which will permit transfer,in close register, of any indicia with ease, speed and reliability andwhich will give consistently good results.

In the earlier days of the art, attention was mainly directed totransfer materials which required the application of water to releasethe indicia. Such transfer materials were usually diiicult to make,complicated in construction, and difficult to store Withoutdeterioration. Moreover the necessity for using a liquid to effect thetransfer gave difficulties in their application and in some casesrendered them useless for desired purposes.

In more recent years attention has been directed to the production oftransfer materials from which the indicia could be transferred withoutthe use of any treatment liquid, so called dry transfer materials. lnsome such materials heat is required in order to release the indiciafrom the carrier support, e.g. for the purpose of softening a waxyrelease layer. It has also been proposed, more recently, to apply to thesurface of the indicia a pressure sensitive adhesive so that theindicia, being very firmly adherent to the pressure sensitive adhesivelayer would release from the carrier support and adhere, with the saidadhesive, to another support.

In general, with this latter type of product it has been necessary toprovide a protective sheet over the pressure sensitive adhesive, whichsheet was peeled away as a step immediately prior to the transfer of theindicia to auother support. The protective sheet was necessary sinceotherwise the transfer material was impossible to handle as a commercialarticle owing to its readiness to stick to anything placed in contactwith it, i.e. sheets of such material could not be stacked for packingpurposes. Moreover the necessity for removing the protective sheetimmediately before using the transfer material led itself to two majordifficulties. On the one hand the actual operation of removing theprotective sheet not infrequently pulled away from the carrier sheet thepressure sensitive adhesive and part, or the whole, of the indicia and,on the other hand, even if the protective sheet was peeled off withoutdamage to the other layers it left a material which because of itsreadiness to stick to anything on the lightest contact could not easilybe manipulated to position it for accurate register of the indicia tothe surface where it was required.

lf it is provided that the pressure sensitive adhesive is present onlyin register with the elements of the indicia this diliiculty is overcomebut in practice it is extremely ditiicult to maintain exact register insuccessive printing operations and it usually arises that the indiciatransfers with an edging of imperfectly registered adhesive. This edgeis unsightly and, being tacky, tends to pick up dirt ICC after transferso that the transferred indicia may become spoilt in a very short timeby the accretion of dirty marks round the elements of the indicia.

Absolute accuracy of register is diicult to achieve so that such methodshave usually only been employed where the indicia are of very simpleform, e.g. straightforward geometrical designs.

Furthermore, dry transfer materials of the type just discussed haveusually used a paper carrier support, sometimes a laminar product of afair degree of complication, which has had a very limited transparencyor transluceney (if indeed it was not opaque) so that accuratepositioning of the transfer material, when the transfer is beingeffected, is the more difficult. Moreover, such carrier sheets based onpaper have often suffered from the disadvantage of dimensional variationwith atmospheric conditions, and have often had a serious tendency tocurl.

As a result of very considerable research and experiment it has beenfound possible to overcome the aforesaid diiculties and it is a primaryobject of the present invention to provide a form of transfer materialwhich is stable on storage, very simple indeed to use and which givesconsistently good transfers.

According to the present invention there is provided a transfer materialcomprising a light transmitting extensible base sheet printed withindicia on one face and said indicia supercoated with an adhesive, theadhesive being of a character which will not adhere to another surfaceunder light linger pressure but which will adhere to another surfacewhen a substantial pressure is applied to the reverse side of the basesheet, whereby when the base sheet is subsequently lifted away theindicia remains, stuck by the adhesive, on said other surface. In thisaspect of the present invention, this application is acontinuation-in-part of my copending application Ser. No. 787,756, filedJanuary 19, 1959, now abandoned.

More specifically according to the present invention there is provided atransfer material comprising a carrier sheet consisting of a sheet oftransparent or translucent iilm of high dimensional stability undernormally varying conditions of temperature and humidity but which isreadily capable of stretching on application of tension thereto, indiciain printing ink carried by said carrier sheet, said printing ink beingbased essentially on a polymeric material and containing a plasticisertherefor, and a thin layer of a pressure sensitive adhesive in registerwith said indicia or extending over the Whole of the printed area of thecarrier sheet on the printed side, the adhesion between the said indiciaand the carrier sheet being reducible by local stretching of the carriersheet in the region thereof, and the pressure sensitive adhesive beingsubstantially non-bonding at pressures less than 50 lbs. per squareinch.

lt is to be noted that if, in a transfer material according to thepresent invention the pressure sensitive adhesive layer is omitted, thenthe application of local pressure to the reverse side of the carriercauses the printed indicia to separate integrally from the carriersheet. This result is achieved by selecting a carrier sheet which isreadily capable of stretching on application of tension thereto andformulating the ink so that the indicia Will so separate on the localapplication of stretching tension to the carrier sheet, i.e. the effectof such stretching must be to apply a force to the indicia which isgreater than the adhesive force between the indicia and the support.

There is thus a fundamental difference between the transfer materialsemployed in the application of an important aspect of the presentinvention and those of the prior art referred to above. The prior artmaterials have relied essentially on the use of a surface adhesive ofgreater adhesive power to the transfer surface and to the indicia thanthe adhesive power of the nd-icia to the carrier, i.e. the surfaceadhesive has acted to pull the indicia away from the support and hold itto the transfer surface. In the preferred materials of the presentinvention, in contrast, the separation of the indicia from the supportderives essentially from a manipulation of the support and not by thepulling power of some applied adhesive, and the thus-loosened indiciaare simply stuck by the high pressure adhesive to the transfer surface.In consequence it is made possible to employ an adhesive which is not abonding adhesive at low pressures.

Transfer materials according to the present invention are easy to handlesince the pressure sensitive adhesive will not bond to anything withwhich it comes into contact unless a substantial pressure is applied. Itis accordingly not necessary to provide a protective sheetsemi-permanently stuck to the adhesive surface. It is desirable inpractice to interleave the transfer materials with, for example,silicone-treated interleaving paper but this paper does not sticktightly to the adhesive layer and will usually separate under its ownweight.

Furthermore, the transparency or translucency of the support sheetenables the transfer material to be accurately positioned for use sincethe ind-icia can be seen through the back of the sheet. The wholeproduct is stable under normal storage conditions and when required foruse it is only necessary to apply it to the surface on to which thetransfer is to be made, and apply a pressure in excess of 50 lbs. persquare inch to the back of the carrier. The indicia then release fromthe support sheet and become adherent to the said surface. In practiceit is usually necessary only to apply pressure to the back of the sheetwith a hard object in the area of the indicia, covering at least part ofthe perimeter of the elements of the indicia, using a suicient pressureto effect the release and simultaneous bonding.

When the adhesive is superimposed on the printed indicia only, and inaccurate register therewith, there is no danger of its being transferredto form an edging to the transferred indicia which may pick up dirt.

If the adhesive is applied as a thin layer over the whole surface of theprinted side of the carrier it is found that, provided it has a lowertensile strength than that of the printing ink and good adhesion to thenon-printed areas of the carrier, it will shear round the elements ofthe printed indicia so that only the adhesive coated on the printedindicia will transfer.

Whilst various types of translucent or transparent film materials aresuitable for use as carrier sheets in the present invention, it is foundthat particularly good results are obtained by the use ofself-supporting films formed of polyalkylene derivatives, e.g.polyethylene, polypropylene and copolymers containing at least 90% ofeither of these polyalkylenes.

The preferred material for use is polyethylene film made of polyethyleneof density 0.96 g./ml., melt index 0.2 (method of BS 1972); softeningpoint 122 C. for 30 deflection (BS 1493); tensile strength 4200 p.s.i.(BS 2571); elongation at break 100-500%; Young modulus 2.0 105 p.s.i.;and water absorption less than .01% after 30 days immersion. The abovepolymer has a different molecular structure to conventionalpolyethylene, having linear and more regular polymer chains with verylittle side chain branching, which impart a high degree of crystallinityof about 93%. This structure provides the physical and chemicalproperties required for use in the present invention namely, stiffness,strength and elongation in very thin film form, and resistance totemperature, Water and solvents.

The film support may be, for example, of thickness 0.001 to 0.008 inchand may have a glossy, matt or semi-matt surface and the transferredindicia will have a corresponding surface. A matt surface to thetransferred indicia is sometimes of value where the transferred image isto ce used for photographic reproduction.

The indicia are applied to the carrier support sheet by a printingoperation. importance in order that it should meet the requirements setforth above, i.e. that it should adhere suflciently to the support andyet be freed from the support by localised stretching of the support.The ink consists essentially of a high polymer and a plasticisertherefor. Generally it is found desirable to select a high polymerwhich, if used alone, would release spontaneously from the support andthen to add to it suflcient of a plasticiser as to achieve the desiredlevel of adhesion to the support.

Thus, for example, a clear ink medium may be prepared from a highpolymer of cellulose nitrate of extra low, low or medium viscosity type,being an ester soluble grade, of nitrogen content of 11.8-12.3%, or aspirit soluble grade of nitrogen content 10.5% to 11.2%. The cellulosenitrate may be employed damped in butanol, or the like, with 65 to 70%polymer solids. The cellulose nitrate is dissolvedin a solvent suitablein volatility for the particular printing process, and which does notdissolve, curl or distort the carrier sheet. Aliphatic or aromatichydrocarbon solvents are undesirable, but esters, ether-esters, ketones,alcohols, ether-alcohols, ketonealcohols are suitable on thepolyethylene carrier support referred to above. A particularly suitablesolvent for screen process printing, having low odour and a lowevaporation rate, is ethylene glycol monoisopropylether acetate. A highpolymer solution as thus formulated provides the necessary tensilestrength of the dry ink film, but used without the inclusion ofplasticiser would give indicia which would spontaneously release fromthe carrier sheet.

A plasticiser must be added rto the high polymer solution .to impartflexibility according to the known principles of lacquer formulation andalso to control the release to precisely the required value by a mostcareful control of concentration. Two types of plasticiser may be used;one type is the so called solvent plasticiser which may provide part ofthe plasticiser content and is usually a nonapolymerio material of lowvolatility, usually an ester, Iwhich `is compatible with the highpolymer and has a softening or dissolving action on it. Examples are,dioctyl phthalate, tributylcitrate, dimethylcyclohexyl adipate,trixyleneylphosphate. The second :type of plasticiser is a non-dryingoil (i.e., non-oxidising) modified polyester, compatible with the highpolymer. The following oils, alcohols and acids may be variouslyemployed in the production of such polyesters:

Oil Alcohol Acid Castor oil. Ethylene glycol. Plthilif (or anhyri eHydrogenated Glycerol. Isophthalic.

castor oil. Coconut oil. Pentaerythritol. Terephthalic.

Trimethylopro- Adipic.

pane.

Sebacic.

A particularly :advantageous plastiser is a polyglyceryl sebacate, of72% castor oil content and having a viscosity x-y, Gardner-Holdt scale.

In general terms, using cellulose nitrate as the polymer there may beused, for parts of cellulose nitrate, 20 to parts of plasticiser, e.g.55 to 150 parts of a castoroil modified alkyd resin or hydrogenatedcastor-oil modified alkyd resin.

The printing inks used may be clear or pigmented or dyed and it is foundto be particularly advantageous to formulate them so that they may beapplied by silk-screen printing methods.

It will generally be found sufficient to so formulate lthe ink that itwill adhere -to the carrier sheet at pressures below 2 lbs. per squareinch but will release from the The formulation of the ink is ofV carriersheet at pressures of 50 lbs. per square yinch or more.

If desired the printed indicia, which may be a clear non-pigmented ink,may be overprinted with a normal type printing ink applied by anyconventional method, e.g. by screen process, letterpress, offset litho,gravure, flexographic or bronzing processes, and this overprinting mayconstitute Ithe means whereby colouration or opacity -is imparted =tothe indicia.

'Ihe pressure sensitive adhesive is preferably applied as a solution,dispersion, or emulsion in organ-ic solvent or water of a mixture of ahigh tack pressure-sensitive adhesive component and a non-tacky lowtensile strength deformable component. The tacky component may be, yforexample, an acrylic, methacrylic ester or acid polymer or copolymer, avinyl ether or ester polymer or copolymer, poly isobutylene orpolybutene.

The non-tacky component may bea saturated long chain hydrocarbon lorcarboxylic acid ester or amide thereof or polymer of any of these or along chain alcohol or a poly glycol.

The following example serve to illustrate the invention:

Example ether acetate 12,500 72% castor oil glyceryl sebacate 2545Dimethylcyclohexyl adipate 255 The polymer .to total plasticiser ratio(which controls the release properties) is 100:67 in this ink.

A modication of this ink to include pigment is achieved by the additionof v6000 parts of rutile titanium dioxide and adjustment of the polymerto total plasticiser ratio to 100:81.

Such clear or pigmented ink medium is printed through a 180 stainlesssteel or nylon mesh screen, the design being formed by a hand cutstencil for simple designs and a photostencil for complex designs, toprovide a dry ink fllm thickness `of 0.0005 i0.0002 inch, on apolyethylene film (polyethylene density 0.96 referred to above).

A high-pressure sensitive adhesive is formulated -as follows. An aqueousemulsion -is formed of 2 parts of an ester of a polyhydric alcohol .anda fatty acid (e.g. ethylene glycol and lauric, palmitic Ior stearicacid) in 12 parts of water. To this is added 5 parts of an emulsion madeup of:

Copolymer of butyl acrylate (80%) and methyl methacrylate (20%) 52.0

to form a stable paste product. This is printed by the screen processand dried by evaporation. The resulting layer is of very low tack.

This adhesive may be printed in register with the indicia, but this isunnecessary, and excellent release, bonding and shear around theperimeter of any detail is obtained with an overall coat over the wholesheet or as a number of simple panels over the individual designs. Asuitable wet coating weight is 1.1-2.2 grams per square foot whichcorresponds to a Wet thickness of .0005-.001 inch.

A discontinuous coating, in which the coating is applied in a largenumber of small discreet -dots cover-ing say 70% of the sheet and with afrequency of 180 per linear 6 inch provides .ease of vrelease andexcellent shearing even `at thick coats `or with adhesives of highershear strength than that just described.

'I'he resulting transfer material may be used in the following manner:

The transfer material is placed, adhesive side down, onto the surfacewhich is to receive the indicia, such as a sheet of drawing paper orfilm. The indicia is registered with the surface and then pressure isapplied using a standard ball-point pen having a .040 finch diameterball, using a light writing load of 2 ozs. constitutes an aver agepressure of 1600 p.s.i., since the pressure band is of .OlO inch width,yand causes a noticeable stretch in the carrier sheet which exceed theyield point of the film and can be seen and felt when the pressure isreleased. The pressure is applied as a series of strokes over at leastpart of th perimeter of each -ink area, :when uni-directional liftingaway of the `carrier film is desirable. yIf pressure is `applied overthe whole of the perimeter of ink area the carrier lm may be lifted awayin any direction.

In practice a load of l to 4 ozs. is adequate, the lightest load beingadequate when the final surface is very soft and permits a largestretching of the carrier sheet and the higher loads when the finalsupport is hard, e.g. glass.

The presently preferred form of dry transfer of the present invention,and its method of use, are shown in the accompanying drawing in whichFIGURE 1 shows a diagrammatic section of the dry transfer materials;

FIGURE 2 shows in section the method and mechanism of transfer;

FIGURE 3 shows the result of the transfer operation, illustrating theresidual elements of the transfer material in their new location.

Referring to these drawings, in FIGURE l there is shown the carrier film1 carrying indicia 2 (one such is shown) and adhesive 3. It Will henoted that the adhesive extends beyond the margins of the indicia tooverlap onto the carrier film 1.

To effect the transfer, the dye transfer material is laid down with thesurface of adhesive layer 3 in contact with a receiving sheet 4.Pressure is applied to the area of the carrier film 1 behind the indicia2 by means of a ball point pen 5. The effect is to stretch the lm 1 asshown and thus release the indicia 2 from the film 1. Air thus entersbetween the indicia 2 and the film 1.

The dry transfer material is then lifted away as shown in FIGURE 3. Thearea of adhesive 3 which overlapped onto the film 1 remains in positionon the carrier lm 1 due to shearing of the adhesive around the edges ofthe indicia. The indicia 2 however is adherent to the receiving sheet 4by means of that part of the adhesive 3 which lay over the indicia 2.

I claim as my invention:

1. As a new article of manufacture, a dry transfer sheet for applyingprinted indicia to a receiving sheet at a selected position on suchreceiving sheet under control of a user, said dry transfer sheetcomprising a carrier sheet of polyethylene having high-releaseproperties; indicia on said polyethylene carrier sheet in the form ofink films strong enough to retain their shape during transfer and havinga mechanically breakable bond to said carrier sheet; a dry adhesivecoating extending over the indicia, said coating being adherable to aselected position on a receiving sheet at ambient conditions uponrubbing with high localized force-per-unit-area over such position butsaid coating being immune to transfer-effecting adhesion uponapplication of light iinger pressure at such position or over otherportions of the transfer sheet, said adhesive coating having a greaterainity for a receiving sheet when subjected to high pressure as byrubbing with a stylus over a selected area thereof than the affinitybetween the indicia and the carrier sheet after application of suchpressure, so that the transfer sheet can be placed against a receivingsheet and adjusted to accurately locate indicia to be transferred in anyselected position on the receiving sheet without adhesion of theadhesive coating to the receiving sheet and thereafter the indicia canbe transferred dry by rubbing as aforesaid while in the selectedposition.

2. As a new article of manufacture, a dry transfer sheet for applyingprinted indicia to a receiving sheet at a selected position on suchreceiving sheet under control of a user, said dry transfer sheetcomprising a light-transmitting carrier sheet at least one surface ofwhich has high-release properties; indicia on the high-release surfaceof said carrier sheet in the form of ink films strong enough to retaintheir shape during transfer and having a mechanically breakable bond tosaid high-release surface of said carrier sheet; and a dry adhesivecoating extending over the indicia, said coating being adherable to aselected position of another sheet at ambient conditions upon rubbingwith high localized force-per-unit-area over such posiition but saidcoating being immune to transfereffecting adhesion upon application oflight finger pressure at such position or over other portions of thetransfer sheet; said adhesive coating having a greater ainity for areceiving sheet when subjected to high pressure as by rubbing with astylus than the affinity between the indicia and the carrier sheet afterapplication of such pressure, so that the dry transfer sheet can beplaced against a receiving sheet and adjusted to accurately locateindicia to be transferred in any selected position on the receivingsheet without adhesion of the adhesive coating to the receiving sheetand thereafter the indicia can be transferred dry while in the selectedposition by rubbing with high localized pressure over the indicia.

3. A transfer sheet, including a carrier sheet having a surface of abond-resisting nature, indicia formed of coherent lms capable ofretaining their shape during transfer and having a mechanicallybreakable bond to the carrier sheet, and a coating of a eXiblelight-transmitting adhesive substance on said indicia having inadequateadhesion to a receiving sheet to effect transfer of said elements underlight finger pressure but having transfer-effecting adhesion to thereceiving sheet under heavy localized pressure equal to that produced byrubbing with a stylus while other elements on the transfer sheet notsubjected to such heavy localized pressure remain on said carrier sheet,whereby said transfer sheet can be freely moved about relative to areceiving sheet to an accurately adjusted position while in contact wtihthe receiving sheet, and heavy localized pressure can then be appliedfor transferring the indicia to an accurately determined position on thereceiving sheet by localized pressure as aforesaid.

4. The method of applying printed indicia to a receiving sheet,including the steps of printing indicia on a carrier sheet with printingmaterial that forms indicia u that are strong enough to retain theirshape during transfer, the carrier sheet and the printing material being-related to provide a mechanically breakable bond between the indiciaand the surface of the carrier sheet; coating the indicia with anadhesive substance that does not cause transfer of the indicia to saidreceiving sheet under light finger pressure; thereafter placing areceiving sheet Vin confronting relation to the carrier sheet andadjusting the indicia to be transferred to a desired position onsaidreceiving sheet and with the adhesive substance which covers the indiciabeing in contact with the receiving sheet; rubbing a stylus over theindicia to be transferred and separating said sheets to effect the drytransfer of said indicia to the desired position on the receiving sheet.

5. The method of applying printed indicia to a receiving sheet,including the steps of printing indicia on a carrier sheet with printingmaterial that forms indicia strong enough to retain their shape duringtransfer, the carrier sheet and the printing material being related toprovide a mechanically breakable bond between the indicia and thesurface of the carrier sheet; coating the printed indicia with anadhesive substance that does not cause transfer of the indicia to saidreceiving sheet under light finger pressure; thereafter placing areceiving sheet in confronting relation to the carrier sheet with theindicia to be transferred at a desired position of said 4receiving sheetand with the adhesive substance which covers the indicia being incontact with the receiving sheet, said sheets being chosen so'that atleast one sheet is light-transmitting to facilitate the adjustment ofthe indicia to be transferred to the desired position on the receivingsheet, rubbing a stylus over the indicia to be transferred andseparating said sheets to effect the dry transfer of the indicia to thedesired position on the receiving sheet.

References Cited in the file of this patent UNITED STATES PATENTS1,820,867 Crowder Aug. 25, 1931 1,946,865 Kubin Feb. 13, 1934 1,963,778Crowder .lune 19, 1934 2,254,072 Jenkins Aug. 26, 1941 2,558,803Wittgren July 3, 1951 2,611,313 Keller et al. Sept. 23, 1952 2,626,226Adair Jan. 20, 1953 2,627,486 Smith Feb. 3, 1953 2,777,781 Kordig et alJan. 15, 1957 3,013,917 Karlan et al. Dec. 19, 1961 3,043,732 ShepherdJuly 10, 1962 OTHER REFERENCES Modern Plastics Encyclopedia for 1959,pp. 112 and 113 cited, October 1958-.

1. AS A NEW ARTICLE OF MANUFACTURE, A DRY TRANSFER SHEET FOR APPLYINGPRINTED INDICIA TO A RECEIVING SHEET AT A SELECTED POSITION ON SUCHRECEIVING SHEET UNDER CONTROL OF A USER, SAID DRY TRANSFER SHEETCOMPRISING A CARRIER SHEET OF POLYETHYLENE HAVING HIGH-RELEASEPROPERTIES; INDICIA ON SAID POLYETHYLENE CARRIER SHEET IN THE FORM OFINK FILMS STRONG ENOUGH TO RETAIN THEIR SHAPE DURING TRANSFER AND HAVINGA MECHANICALLY BREAKABLE BOND TO SAID CARRIER SHEET; A DRY ADHESIVECOATING EXTENDING OVER THE INDICIA, SAID COATING BEING ADHERABLE TO ASELECTED POSITION ON A RECEIVING SHEET AT AMBIENT CONDITIONS UPONRUBBING WITH HIGH LOCALIZED FORCE-PER-UNIT-AREA OVER SUCH POSITON BUTSAID COATING BEING IMMUNE TO TRANSFER-EFFECTING ADHESION UPONAPPLICATION OF LIGHT FINGER PRESSURE AT SUCH POSITION OR OVER OTHERPORTIONS OF THE TRANSFER SHEET, SAID ADHESIVE COATING HAVING A GREATERAFFINITY FOR A RECEIVING SHEET WHEN SUBJECTED TO HIGH PRESSURE AS BYRUB-